From 6d2ed7484a29e5a093f24dd5fbbe3522029b4816 Mon Sep 17 00:00:00 2001
From: "B. Watson" <urchlay@slackware.uk>
Date: Sun, 15 Dec 2024 05:06:41 -0500
Subject: implement -s and -S (seek) options.

---
 uxd.c | 69 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 66 insertions(+), 3 deletions(-)

(limited to 'uxd.c')

diff --git a/uxd.c b/uxd.c
index c235777..866ad78 100644
--- a/uxd.c
+++ b/uxd.c
@@ -42,6 +42,10 @@ extern int optind;
 #define VERSION "(unknown version)"
 #endif
 
+#ifndef BUFSIZ
+#define BUFSIZ 4096
+#endif
+
 /* ANSI colors */
 #define BLACK  0 /* don't use (could be the background color) */
 #define RED    1
@@ -77,7 +81,8 @@ int bold = 0; /* -b */
 int hilite_multi = 0; /* -r */
 int mono = 0; /* -m */
 long display_offset = 0; /* -o */
-long seekpos = 0; /* -s */
+long seekpos = 0; /* -s, -S */
+int seek_offset_zero = 0; /* -S */
 long limit; /* -l */
 const char *hex_byte_fmt = "%02x";   /* -u */
 const char *hex_word_fmt = "%04x: "; /* "  */
@@ -121,7 +126,7 @@ void parse_options(int argc, char **argv) {
 			version();
 	}
 
-	while((opt = my_getopt(argc, argv, "bl:rmo:s:uhv")) != -1) {
+	while((opt = my_getopt(argc, argv, "bl:rmo:S:s:uhv")) != -1) {
 		switch(opt) {
 			case 'b':
 				bold = 1; break;
@@ -133,8 +138,12 @@ void parse_options(int argc, char **argv) {
 				mono = 1; break;
 			case 'o':
 				display_offset = parse_number(optarg); break;
+			case 'S':
+				seek_offset_zero = 1;
+				/* fall thru */
 			case 's':
-				seekpos = parse_number(optarg); break;
+				seekpos = parse_number(optarg);
+				break;
 			case 'u':
 				hex_byte_fmt = "%02X"; hex_word_fmt = "%04X: "; break;
 			case 'h':
@@ -381,7 +390,61 @@ int dump_utf8_char(void) {
 	return 1;
 }
 
+/* this only gets called when reading stdin. */
+void skip_input(unsigned int bytes) {
+	char tmp[BUFSIZ];
+
+	if(fread(tmp, 1, bytes, input) < bytes) {
+		if(feof(input)) return;
+
+		/* this probably never happens when reading from stdin: */
+		fprintf(stderr, "%s: ", self);
+		perror("fread()");
+		exit(1);
+	}
+}
+
+/* this only gets called when reading stdin. */
+void fake_seek(void) {
+	long i = seekpos;
+
+	while(i >= BUFSIZ) {
+		skip_input(BUFSIZ);
+		if(feof(input)) return;
+		i -= BUFSIZ;
+	}
+
+	skip_input(i);
+}
+
+/* used by -s option */
+void seek_input(void) {
+	int whence = SEEK_SET;
+
+	if(seekpos < 0) {
+		whence = SEEK_END;
+	}
+
+	if(fseek(input, seekpos, whence) == 0) {
+		filepos = ftell(input);
+		return;
+	}
+
+	/* fseek() failed, likely we're reading stdin. fake it, if we can. */
+	if(whence == SEEK_SET) {
+		clearerr(input);
+		fake_seek();
+		filepos = seekpos;
+	} else {
+		perror(self);
+		exit(1);
+	}
+}
+
 void dump_file(void) {
+	if(seekpos) seek_input();
+	if(seek_offset_zero) filepos = 0;
+
 	while(dump_utf8_char())
 		if(limit && (filepos >= limit)) break;
 
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